U.S. application Ser. No. 11/656,563, filed on Jan. 23, 2007 and published as US published application 2007/0196704 A1 and incorporated herein by reference in its entirety, describes a fuel cell system 100 in which the solid oxide fuel cell (SOFC) stacks are located on a base, as shown in FIG. 1. Wedge shaped ceramic side baffles 220 (e.g., having a non-uniform thickness and a roughly triangular cross sectional shape in the horizontal direction) are located between adjacent fuel cell stacks 14 (or columns of fuel cell stacks). The baffles 220 serve to direct the cathode feed into the cathode flow paths and to fill the space between adjacent stacks so that the cathode feed passes through each of the stacks 14, rather than bypassing around the longitudinal sides of the stacks 14. The baffles 220 are held in place by tie rods 222 that pass through closely fitting bores 224 centrally located in each of the baffles 220. Preferably, the baffles 220 are electrically non-conductive and made as one unitary piece from a suitable ceramic material. FIG. 1 also shows fuel distribution manifolds between the stacks in the stack column and fuel inlet and exhaust conduits connected to the manifolds.
In this prior art system, the SOFC stacks maintain a compressive load. The compressive load is maintained by upper pressure plate 230, tie rods 222, lower pressure plate 90 and a compression spring assembly located below the lower pressure plate 90. The compression spring assembly applies a load directly to the lower pressure plate 90 and to the upper pressure plate 230 via the tie rods 222.
FIG. 2 illustrates another prior art fuel cell stack assembly 200 described in U.S. application Ser. No. 15/008,726, filed on Jan. 28, 2016 and published as U.S. published application US 2016/0226093 A1 and incorporated herein by reference in its entirety. Referring to FIG. 2, the fuel cell stack assembly 200 includes a fuel cell stack column 140, side baffles 220 disposed on opposing sides of the column 140, a lower block 503, and a compression assembly 600 including an upper block 603. The column includes three fuel cell stacks 14, fuel manifolds 204 disposed between the fuel cell stacks 14, and termination plates 27 disposed on opposing ends of the column 140. The fuel cell stacks 14 include a plurality of fuel cells stacked upon one another and separated by interconnects. A plurality of the fuel cell stack assemblies 200 may be attached to a base 239, as shown in FIG. 1.
An exemplary fuel manifold 204 is described in the U.S. application Ser. No. 11/656,563 noted above. Any number of fuel manifolds 204 may be provided between adjacent end plates of adjacent fuel cells of the fuel cell stacks 14, as desired.
The side baffles 220 connect the upper block 603 of the compression assembly 600 and the lower block 503. The side baffles 220, the compression assembly 600, and the lower block 503 may be collectively referred to as a “stack housing”. The stack housing is configured to apply a compressive load to the column 140. The configuration of the stack housing eliminates costly feed-throughs and resulting tie rod heat sinks and uses the same part (i.e., side baffle 220) for two purposes: to place the load on the stacks 14 and to direct the cathode feed flow stream (e.g., for a ring shaped arrangement of stacks shown in FIG. 1, the cathode inlet stream, such as air or another oxidizer may be provided from a manifold outside the ring shaped arrangement through the stacks and the exit as a cathode exhaust stream to a manifold located inside the ring shaped arrangement). The side baffles 220 may also electrically isolate the fuel cell stacks 14 from metal components in the system. The load on the column 140 may be provided by the compression assembly 600, which is held in place by the side baffles 220 and the lower block 503. In other words, the compression assembly 600 may bias the stacks 14 of the column 140 towards the lower block 503.
The side baffles 220 are plate-shaped rather than wedge-shaped and include baffle plates 202 and ceramic inserts 406 configured to connect the baffle plates 202. In particular, the baffle plates 202 include generally circular cutouts 502 in which the inserts 406 are disposed. The inserts 406 do not completely fill the cutouts 502. The inserts 406 are generally bowtie-shaped, but include flat edges 501 rather than fully rounded edges. Thus, an empty space remains in the respective cutouts 502 above or below the inserts 406.
The side baffles 220 and baffle plates 202 have two major surfaces and one or more (e.g., four) edge surfaces. One or more of the edge surfaces may have an area at least 5 times smaller than each of the major surfaces. Alternatively, one or more edge surfaces may have an area at least 4 times or 3 times smaller than at least one of the major surfaces. Preferably, the baffle plates 202 have a constant width or thickness, have a substantially rectangular shape when viewed from the side of the major surface, and have a cross sectional shape which is substantially rectangular. In alternative embodiments, the ceramic side baffles 220 are not rectangular, but may have a wedge shaped cross-section. That is, one of the edge surfaces may be wider than the opposing edge surface. However, unlike the prior art baffles, which completely fill the space between adjacent electrode stacks 14, the side baffles 220 of this embodiment are configured so that there is space between side baffles 220. In other words, the side baffles 220 of this embodiment do not completely fill the space between adjacent columns 140. In other embodiments, wedge-shaped metal baffles may be inserted between adjacent side baffles 220, similar to the configuration shown in FIG. 1.
Generally, the side baffles 220 are made from a high-temperature tolerant material, such as alumina or other suitable ceramic. In various embodiments, the side baffles 220 are made from a ceramic matrix composite (CMC). The CMC may include, for example, a matrix of aluminum oxide (e.g., alumina), zirconium oxide or silicon carbide. Other matrix materials may be selected as well. The fibers may be made from alumina, carbon, silicon carbide, or any other suitable material. The lower block 503 and the compression assembly 600 may also be made of the same or similar materials. If the baffles are made from alumina or an alumina fiber/alumina matrix CMC, then this material is a relatively good thermal conductor at typical SOFC operating temperatures (e.g., above 700° C.). If thermal decoupling of neighboring stacks or columns is desired, then the baffles can be made of a thermally insulating ceramic or CMC material.
Other elements of the compression housing, such as the lower block 503 and the compression assembly 600 may also be made of the same or similar materials. For example, the lower block 503 may comprise a ceramic material, such as alumina or CMC, which is separately attached (e.g., by the inserts, dovetails or other implements) to the side baffles 220 and to a system base 239.
FIG. 3 illustrates another prior art fuel cell stack assembly 300 described in U.S. application Ser. No. 15/008,726. The fuel cell stack assembly 300 is similar to the fuel cell stack assembly 200, so only the differences therebetween will be discussed in detail. Similar elements have the same reference numbers. Fuel rails 214 (e.g. fuel inlet and outlet pipes or conduits) connect to fuel manifolds 204 located between the stacks 14 in the column.
Referring to FIG. 3, the fuel cell stack assembly 300 includes side baffles 220 disposed on opposing sides of the column of fuel cell stacks 14. However, each of the side baffles 220 includes only a single baffle plate 202, rather than the multiple baffle plates 202 of the fuel cell stack assembly 200. In addition, the side baffles 220 include ceramic inserts 406 to connect the baffle plates 202 to a compression assembly 600 and a lower block 503.